On MythBusters, Byron and fellow “Build Team” members Tory Belleci and Grant Imahara assist the hosts Adam Savage and Jamie Hyneman in testing the plausibility of various myths and also host their own segments. She became involved in the show after persistently showing up at Hyneman’s M5 Industries workshop in a desire to get hired by his company. On her first day as a paid employee, she was asked by Hyneman and MythBusters producer Peter Rees to help out with the “vacuum plane toilet” myth, and was asked to model her buttocks for a cast. She and the other “Build Team” members were given a more prominent role beginning with the show’s second season. Not having had a long history in show business, Byron at first found it difficult to act naturally with this more visible position but gradually became more accustomed to it.

During the second half of the 2009 season, Byron was on parental leave from the show. She was temporarily replaced by Jessi Combs.

Kari now also has her own show Head Rush on the Science Channel, geared towards science education and teens.